Process of bonding metal



. y 1945- A. LONGORIA EIAL w m I 1 4 PROCESS OF BONDING METAL Filed March 18, 1942 MJ I frail V I v Patented May 28,1946

FFICE PROCESS OF BONDING METAL Antonio Longoria, South Euclid, and Christian Girl, Madison, Ohio, assig'nors, by direct and mesne assignments, of one-half to said Antonio Longoria and one-half to Unit Rays, Inc., Cleveland, Ohio, a corporation of Ohio Application March 18, 1942, Serial No. 435,216

2 Claims.

This invention relates to a process of bonding metals, and has for its general object to enable metals having different melting points to be bonded together without the migration of a substantial or detrimental proportion of either of the metals into the other. A field wherein the prevention of such migration is particularly important is the production of valves for internal combustion engines, such as those which are employed with airplane engines, wherein the ta.- pered or frusto conical seating portions of the valve heads are provided with rings of an alloy known as Stellite, the said rings being so employed because they possess th properties of being not hard; of being resistant to shock as by impact, a well as resistant to oxidation by the lead content of the high octane fuels used in said engines. It has been found dimcult heretofore to prevent, during the bonding operation, the

detrimental migration of one or more ofthe constituents of the alloy of the valve head from entering intoth alloy of the Stellite ring in such proportion as to render it incapable of retaining, substantially unimpaired, all of the properties which are essential to its continuous satisfactory operation.

It is the general purpose and object of our invention to provide a method for bonding metals of different melting points, and more particularly for bonding Stellite rings to the seating portions of the aforesaidvalve heads, in such manner that any detrimental migration of one or more or the constituents of the alloy of the valve head, into the alloy of the Stellite ring will not occur; also that any detrimental migration of one or more of the constituents of the alloy of the Stellite ring into the alloy of the valve head will not occur.

.As is well known to those familiar with the construction of valves for airplane engines, the alloy of which the heads of these valve are usually composed consists of steel alloyed with nickel and/or chromium; that is to say, the heads of these-valves are made of steel alloyed with nickel and, in the case of valve heads as produced by leading manufacturers for the exhaust valves of airplane motors, these heads also contain chromium. The alloy of which the Stellite rings are composed consists principally ol' cobalt alloyed with chromium, and the proportions of chromium to cobalt may vary from to 50% by weight of the former to in Hackh's Chemical Dictionary. published by P. Blakistons Son 8: Co. Inc. in 1929. in addition,

the weight of the latter, as stated the alloy also usually contains a small percentage of tungsten.

It is well known that the alloys from which the valve heads referred to are made have melting points varying between 2700 F. and 2800" that great care must be taken in the performance of this operation, a certain amount of intermingllng of metal from the valve-head alloy with the Stellite has frequently occurred, such intermingling being of a sufflclent extent to render the latter unsuitable for performing it iiitended functions. We are enabled to prevent metals comprised within a valve-head alloy, such as described herein, as well as those within the Stellite alloy, from migrating from one of such alloys into the other to any substantial or detrimental extent, by interposing, between the tapered seating portion of the said head and the Stellit to be bonded thereto, what we term an lsolator,,said isolator possessing a, melting point higher than that of the Stellite and no higher than, and preferably approximately the same as, that of th valve-head alloy, and having been suitably applied to the seating portion of the valve head previously to the operation of bonding thev Stellite thereto, and said isolator also being capable of forming a satisfactory bond with both the seating portion of the valve head and the Stellite ring.

We have found that certain metals of the ironchromium-cobalt-nickel-manganese group possess melting points higher than that of Stellite and approximating the melting point of the valve head alloy. Of the metal possessing suchmelting point (chromium, cobalt and nickel), our ex perience with chromium shows that it is admirably adaptabl as a bonding isolator, due not only to its ability to form a satisfactory bond between the seating portion of the valve head and the Stellite ring but also because it is itself a constituent, to a large degree, of the alloys of which the valve heads and the Stellite ringsare composed. It can be electrically deposited upon the seating portion of th valve heads; its meltin point is considerably higher than the melting point of Stellite and is substantially the same as the melting point of the alloy steel used in the production of'valve heads. Furthermore, when applied to the seating surfaces of the valve beads by being electrically deposited thereon, it not only provides a covering or coating for said portions, but, as experienc ha shown, is firmly bonded thereto by thepenetration. to a shallow depth, of portions of the inner surfaces thereof into the outer surfaces of the seating portions of the valve heads. When the chromium is applied to the seating portion of the valve head by electrical deposition, the coating or covering is much thicker than that which is ordinarily used for purely protective coverings, being from .005 to .010 inch in thickness.

The chromium coating may be applied only to the seating portions of the'valve heads by protecting the remainder of the valve head surfaces which are immersed in the plating bath with any of the well known matings employed for such purpose; or the whole valve head may be plated and the surplus plating removed during the final machining operations.

It will be obvious that, where the seating portion of the valve body is heated to a temperature whereby the skin thereof becomes softened, th chromium thereon will soften to about the same degree, but without intermingling with the alloy steel of the valve head to any appreciable extent, other than the limited intermingling between the inner skin of the chromium and the outer skin of the valve head necessary to provide a sufllcient bond,

-In carrying out our invent on, we preferably employ the apparatus shown in the drawing hereof, wherein Fig. 1 is a vertical sectional view through th means for supporting and heating the valve body and for supplying heat to the surfac of the tapered frusto conical seating portion thereof, the valve being shown in sectional elevation; and an electric furnace, having means for controlling the temperature thereof and means for automatically cutting oil the supply of current to the peripheral portion of the valve, being shown schematically; Fig. 2 a detail in sectional elevation of the valve head, mold and electrode shown in the preceding view and wherein the Stellite within the mold is in a divided condition; and Fig. 3 a view similar to Fig. 2, but wherein the Stellite is employed in the shape of a preformed ring of the same.

The apparatus shown in Fig. l is substantially identical with that shown, described and claimed in the application of Antonio Longoria, flied February 4, 1942, Serial No. 429,556 (now Patent No, 2,377,163, dated May 29. 1945), and the portions of the apparatus shown in Figs. 2 and 3 are substantially the same a those shown in the application of Antonio Longoria, Serial No. 431,805, filed February 19, 1942 (now Patent No. 2,358,090, dated September 12, 1944) Describing briefly the apparatus shown in Fig. 1, i denotes generally the head of a valve, such as is employed with the engines of airplanes, and I i the stem thereof, the said stem having an enlarged cylindrical lower end I! and being also provided with a tapered or frusto conical seating portion l3, shoulders ll and I5 being shown as provided respectively above and below the said seating portion. It will be understood that the drawing does not show the valve in the final machined condition which it will assume before it may be assembled into an engine. The surplus wall of the bore section ll.

' purpose i graphite.

metal appearing thereon in various place iscilitates the application of the Stellite facin thereto and the machining of said facing, as well as subsequent processing steps.

l5 denotes a block of material possessing high electrical conductivity and incidentally high heat conductivity. The material which we prefer to use is copper, because it possesses high electrical conductivity. As will be noted, this block is of large cross-sectional area, whereby it is capable of carrying a heavy or high current without becoming unduly heated thereby; it is shown as provided with an upper cylindrical bore section I! and a lower cylindrical bore section I! constituting an extension of the upper section but being of les diameter than the same, there being an annular shoulder l9 interposed between the said bore sections.

The upper surface of the block 16 is formed into an inverted frusto conical seat 20, extending outwardly from the upper end of the bore section ll. This seat supports a mold 2! of refractory material, such as lava rock, which will not carburize the metal therewithin and which will not short-circuit the current. The mold is shown as provided with a bore 22 constitutin an extension of the bore section 11. This bore 22 extends preferably upwardly as far as the bottom of the lower shoulder It of the valve head, the said bore being preferably of the same diameter as that of the shoulder. An annular mold cavity 23 is provided between the upper surface of the mold and the peripheral tapered portion of the valve head. The mold is shown as extending above th upper shoulder H of the valve body, for purposes to be described hereinafter.

24 denote a bushing of refractory material fitted within the lower bore section i8 and serving as a means for centering the lower end ll of the valve stem and electrically insulating the latter from the block it.

The shoulder I8 is shown as supporting a plurality of rings 25 of carbon possessing relatively high electrical resistivity and low heat conductivity, the said rings engaging the surrounding upwardly as far as the bottom of the mold II.

28 denotes an electrode in the form of a ring of carbon of high heat resistivity and somewhat lower specific electrical resistivity than the rings 25. The carbon which we prefer to use for this It will be. noted that the ring 20 fits within the bore 22 of the mold and that its upper end is beveled outwardly from the interior thereof, whereby only a limited annular contact area is provided between the top of the ring and the lower shouldered portion ii of the valve head, adjacent to the bottom of the surface of the tapered portion 13 of the valve head. Due to this beveling of the graphite ring, its electrical resistance is greatly increased where it contacts with the valve head.

21 denotes an upper block, preferably of copper, having a large diameter whereby it is capable of carrying a heavy electrical current without being unduly heated thereby.

28 denotes an electrode which is mounted within a cavity'provided therefor in the lower end of the block 21, the said electrode also being preferably of graphite, for purposes explained in connection with the electrode ring 26, and having its 0 lower end formed into an external ring 2! sur- These rings extend portion of the valve head above the shoulder it connection with one of the well-known types of current regulators, to control the temperature of the molten metal in the furnace. K denotes a pyrometer for indicating visually the temperature of the molten metal; it can be used also in connection with hand-operated means for controlling the current which heats the furnace and thereby the temperature of the molten metal. Through the employment of an apparatus such as shown in Fig. 1 and just described, electric current will be supplied throughthe conductors 3|, 32, the conductor blocks I6 and 21 and the rings 22, 25, 26 and 29 through the peripheral portion of the valve head including the chromium'coating X, whereby said coating will become softened to an extent to-enable it to form a bond with molten Stellite introduced into the mold from the furnace F. The chromium coating having thus been rendered suitable for forming a bond with the Stellite and the molten Stellite having been delivered into the mold, the supply of -cur rent is discontinued. The Stellite will become firmly bonded to the chromium and thereby to the portion ii of thevalve head. Should the outer skin or surfac of the portion ii of the valve head become softened during this operadivided condition around the seating portion l3, as shown at 33 in Fig. 2, or may be applied in ring-form to said portiomasshown at 34 in Fig. 3, all of the Stellite in the former case, and at least the portion of the Stellite in contact with the seating surface in the latter case, being melted by raising the outer surface of the portion l3 of the valve head and the chromium plating thereon to a temperature sumcient to render the chromium plating suitable for forming a bond with J the molten Stellite in contact therewith.

, It will be evident that th apparatus shown herein is only illustrative of one means for heating the insulating coating and the tapered seatin portion of the valve head.

It is within the purview of our invention to apply the chromium to the seating portion l3 of the valve head in other manners than by elec tricallydepositing the same thereon. If desirable, it may be formed into a ring of suitable shape to be fitted upon th outer surface of the portion I3; and, when the surface of the said I portion l3 and the surroundin chromium ring are heated to a temperature sufllcient to soften the chromium, it will be firmly bonded to the said portion; and the Stellite may be bonded to said ring at this time, or by a. subsequent heating operation in the manner hereinbefore detion, there will be no substantial intermingling of the chromium with the alloy steel of the valve head, the intermingling being limited to the contacting skin portions of the chromium and the valve head; and the molten Stellite willbe bonded 'to the chromium, but the iron constituent of the valve metal cannot intermingle with the Stellite because of the action of the chromium as an isolator between the Stellite and the valve head, due to the fact that the afllnity between the iron constituent of the valve head and the chromium is greater than the affinity between such iron constituent and the cobalt in the Stellite. However,

and the chromium, this intermingling would be negligible'in its results, since the valv metal contains a substantial percentag of chromium.

Since, as has been pointed out, the chromium has been firmly bonded to the surface It during the electroplating process and since this bonding of the constituents of the valve-head alloy into the Stellite alloy, and also without any substantial or detrimental migration'of. one or more of will be increased during the heating period, and 7 since, further, the latter is in a softened or semisoftened condition, a solid bonding of the Stellite with the metal of the valve head shoud be ef-" fected, and without the undesirable intermlngling of any of the metallic constituents of the stelliteand valve body.

Our methodof interposing an isolator between the Stellite and the seating Portion Il may also the constituents of the Stellite alloy into the valvehead alloy; also without any substantial or detrimental migration of the isolator metal into the Stellite or'into the valve-head alloy.

An important contributory factor to the reallv zation of the objects of our invention is the shortness of time occupied in uniting the metal of lower melting point- (as Stellite) to the metal of higher melting point through the interposed isolator. I

The amount of current necessary to be delivered through the peripheral portions of the valve heads and the chromium coatings thereon in order to eifect the bonding operation within the desired short period of'time will varywith the diameter and other proportions of the heads. Where a valve head of about three-inch diameter is to be provided with a Stellite ring and the v head is of the hollow sodium-cooled type, an

alternating current of approximately 80,000 amps. and 3.15 volts will be effective in raising the temperature of the chromium coating to the desired, degree-to form a bond withthe molten Stellite surrounding the same'in from 12 tom seconds. Under like operating conditions, similar results can be obtained where nickel coatings are employed in place of chromium coatings.

Having thus described our invention, .what we claim is: v v

1. The process of providing a frusto-conical peripheral portion of a valve head consisting of alloyed steel, witha surrounding ring; of cobalt alloyed with chromium and tungsten and having smeltinspointlowerthanthetofthueidfnuw conical peripheral portion. said process comprising the steps of electrically depositing up n said irusto-conical peripheral portion a covering of a metalselected from the group consisting oi chromium and nickel and having a melting point approximating that o! the irusto-conical peripheral portion of the said valve head but higher than that of the said alloy of cobalt, chromium and tungsten; placing the alloy for producing said surrounding ring in contact with, the external surface of the said covering, throughout the entire circumierential extent of the latter; and simultaneously passing a heating electrical current only throughout the peripheral portion of the valve head and the entire extent 0! the covering, thereby to raise the temperature of the latter to a point su mcient to enable the external surface of the same to form a bmd with the portion of the allot of copper, chromium and tungsten in contact therewith, but with no appreciable mingling of the elements or the valve head with the elements or the said alloy surrounding the same.

2. The process of providing a irusto-conical peripheral portion of a valve head consisting of alloyed steel, with a surrounding ring of cobalt alloyed with chromium and tungsten and having a melting point lower than that 0! the said irustoconical peripheral portion, said process comprising the steps of electrically depositing upon said frusto-oonical peripheral portion a covering consisting essentially oi chromium and having a melting point approximating that of the irustoconical peripheral portion oi the said valve head but higher than that of the material 01! which said ring is composed; placing a ring composed oi such alloy oi cobalt with chromium and tungsten in contact with the external surface of the said covering, throughout the entire circumferential extent of the latter; and simultaneously passing a heating electrical current only through the entire peripheral portion of the valve head and the entire covering thereby to raise the covering to a temperature sufllcient to enable the external suriace of the covering to form a bond with the portion of the ring in contact therewith. but with no appreciable mingling of the elements of the valve head with the elements of the said ring.

V ANTONIO LONGORIA.

CHRISTIAN GIRL. 

